... water - something they presumably lack whilst at sea. Your craving for citrus fruits may reflect your body's desire for vitamin C or some other compound, but once this is sated your craving my disappear. My personal take on the "natural" diet is that ancient ancestors living in a forest ...

Obviously with direct labeling you label directly the compound you want to detect, while with indirect labeling you label something else, that probably interacts with the studied compound. maybe a little context would help.

... (listed below) have reported working methods for dating those blood stains. These mainly rely on spectroscopy and the hemoglobin (and other forms) compound. We would like to be initiative and setup some new kind of procedure. We thought about a few things (if you have other ideas, please please ...